Dead Fish Swimming

Like their brothers the sockeye, kokanee are driven by an irresistible urge to spawn. That urge has driven about 200,000 kokanee up the South Fork Boise River, but their way to spawning areas is blocked by a fish control weir about five miles upstream from Pine. The river, nearly 100 yards across here, is teeming with red fish - most of them only 8 to 9 inches long. Most of them will be thwarted in their natural drive, and all of them will die in a few days. It's all in the name of improving the kokanee fishery in Anderson Ranch Reservoir. Idaho Fish and Game managers want to limit the number of fish passing the weir into spawning habitat to about 20,000 fish. "By limiting the number of fish that are spawning, we hope to reduce the number of young produced so the fish grow bigger in the future," Southwest regional fisheries biologist Lance Hebdon said. "Our target is to get spawning kokanee in the 12- to 13-inch range, similar to what we have in Lucky Peak. Kokanee anglers frequently tell us they prefer these larger fish." And by letting them die naturally in the stream they will return nutrients to a system low in nutrients, in turn helping to improve ecosystem health as well as other fisheries. Kokanee are part of the Pacific salmon family, which means they die after they spawn, Hebdon said. Southwest Idaho has four big kokanee fisheries - Anderson Ranch, Deadwood, Arrowrock and Lucky Peak reservoirs. Kokanee are not native to any of these waters and were introduced in all four. Lucky Peak is stocked with hatchery kokanee and provides a solid fishery, with good size fish. Kokanee are trapped at Deadwood Reservoir to collect eggs that are raised in hatcheries and used to supply kokanee fisheries across the state, including Lucky Peak, Ririe and Devils Creek Reservoirs and Coeur d'Alene Lake. This is the first year Idaho Fish and Game has installed the fish barricade on the South Fork as part of the statewide kokanee management program. The weir lets Fish and Game control the number of kokanee that are going up river to spawn. "We've created these fisheries in this artificial habitat," Hebdon said. "And what frequently happens in these kokanee fisheries if we have large areas where they can spawn naturally, the average size goes down substantially, to where you get spawning fish in the 6- to 8-inch range." Fish and Game is trying to keep most of the kokanee from reaching good spawning habitat, in hopes of reducing kokanee densities in the reservoir. Because the more kokanee there are in a reservoir, the smaller the fish are when they mature. Managing for an average 12-inch fish maintains good catch rates for kokanee while allowing some fish to grow to larger sizes. "We need to reduce the number of kokanee in Anderson Ranch Reservoir to bring growth rates back up," Magic Valley regional fishery manager Doug Megargle said. But fish limits haven't changed. "We didn't change any limits on the stream," he said. "It's still a six-fish limit for kokanee." In the lake, anglers can catch 25, but once they hit the stream, they can catch six fish. Fishing is closed about 100 yards upstream and downstream from the weir for personal safety reasons and to reduce the temptation to resort to snagging. Managers want the rest of the fish to die in the stream. The Boise and Payette river systems are fairly high elevation systems and geologically naturally low in nutrients, Hebdon said. Historically salmon and steelhead would come into these systems and spawn and die, bringing nutrients from the ocean. But the kokanee introduced into the reservoir systems have taken the place of salmon and steelhead that now are blocked by dams. "They are providing nutrients to a system that is naturally low in nutrients," he said. The kokanee have a two- to three-year life cycle and, like salmon, they migrate upstream into smaller streams to spawn and die. Kokanee in the reservoir are silvery green. At the start of the spawning run, the males will develop a greenish head and bright red to reddish-orange body. The females will get slightly red. Once the fish have changed into their spawning colors and started to move upstream, they will either die at the weir or 10 to 12 miles up river in seven to nine days. "It gives everything it's got to make the spawning run," Megargle said. "It stops feeding. Essentially its final mission is to spawn and then pass on." The kokanee bring a lot of nutrients back up from the reservoir. When they die they decompose in the river, and all the nutrients in them - nitrogen, phosphorous, carbon - are released back into the ecosystem. The weir opened in mid-August and will run into early or mid-October. "It depends on when the run ends," Megargle said. "We are going to run it until kokanee aren't running anymore."